Charge forming device



Jan. 26, 1937. F. E. ASELTINE CHARGE FORMING DEVICE Filed Sept. 14, 1933 I J MS Z-IwENTOR BY QQW/MAM as ATTORNEY Patented Jan. 26, 1937 PATENT OFFICE CHARGE FORMING DEVICE Fred E. Aseltine, Dayton,

Ohio, assignor, by

mesne assignments, to General Motors Corporation, Detrolt, Mich., a corporation of Delaware Application September 14, 1933, Serial No. 689,351

26 Claims.

This invention relates to charge forming devices for internal combustion engines and more particularly to that type of charge forming device which comprises a plurality of primary mixing chambers, one for each intake port of the engine and which cooperate respectively with a plurality of secondary mixing chambers located adjacent the said intake ports and receiving a primary mixture of fuel and air from conduits connected with the primary mixing chambers while receiving air when required through an air manifold having a single air inlet for supplying air to all of the secondary mixing chambers.

An example of a charge forming device of this I character is disclosed in the patents to Fred H. Aseltine et a1., 1,913,741, issued June 13, 1933, and 1,537,938 issued December 5, 1933. The present invention is illustrated herein as embodied in a charge forming device of the general character shown in these patents.

In the device disclosed in the above application and in earlier devices of similar character, various means have been provided to control the proportions of fuel and air in the mixture under various operating conditions for the purpose of supplying to the engine a mixture having the desired fuel and air ratio to properly operate the engine under any and all operating conditions. Among these proportioning devices are certain structures for regulating the mixture proportions by variably controlling the admission of air and it is one object of the present invention toprovide means for restricting the admission of air to the carburetor tosome extent during operation following opening of the throttle at low and intermediate speeds and means for reducing the effect of this restricting means at relatively high speeds for the purpose of forming a somewhat leaner mixture at such high speeds. This object is accomplished by the provision of an auxiliary air valve which is opened by engine suction and a dash pot to retard the opening movement of such air valve, the dash pot being fully effective until the throttle approaches its fully opened position when said throttle operates means to reduce the retarding effect of the dash pot so that upon further opening of the throttle the opening of the auxiliary air valve is retarded to a lesser degree and consequently the valve will open more freely to admit a greater quantity of air upon opening of the throttle as the latter approaches fully open position.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. 1 is a vertical, longitudinal section through a charge forming device in which the present invention is embodied.

Fig. 2 is a fragmentary, transverse, vertical section on the line 2-2 of Fig. 1 showing the pump delivery conduit diagrammatically in dotted lines.

Fig. 3 is a fragmentary side elevation showing the throttle actuating mechanism.

The charge forming device comprises a carburetor unit which is adapted to be connected toan air manifold which has a plurality of outlet branches adapted to be connected to the engine block and communicating with the several engine intake ports. For the sake of simplicity, the manifold is not illustrated herein and the drawing shows only the carburetor unit itself.

This carburetor unit comprises a main housing 20 having an attaching flange 22 adapted to be secured to the manifold by machine screws. An air inlet coupling 24 is secured in position to register with an opening in the upper wall of the housing 20 in any suitable way. A casting 26, having certain dash pot chambers and fuel passages formed therein, is secured by screws to the lower wall of the housing 20 and a sheet metal fuel bowl 28 is held tight against an annular shoulder 30 formed on the housing 20 by a screw 32 which is screwed into the casting 26. Fuel is conducted from a main source of supply to the fuel bowl through a conduit (not shown) and the flow of fuel to the bowl is controlled by a float (not shown) which operates in the usual manner to maintain a substantially constant level of fuel in the bowl. Fuel flows from the bowl 28 to a plurality of primary fuel nozzles 34, one of which is located in each of the primary mixing chambers 36, the construction of which is briefly described hereinafter. The fuel conduit between the fuel bowl and thenozzle comprises a vertical fuel passage 38 com- ,municating at its upper end with a horizontal fuel canal 40 which connects with each of the nozzles 34 through orifices 42. Fuelis admitted from the fuel bowl to the passage 38 at all speeds through a fixed metering orifice 44 and at high speeds additional fuel is supplied through an orifice 46 controlled by a valve 48 in the manner set forth in the above mentioned Patent 1,937,938.

Fuel is lifted from the fuel bowl through the above described fuel passages and primary fuel nozzles to the mixing chambers by the suction therein. Closing movements of the throttle cause a reduction in mixing chamber suction which might permit the fuel column to drop sufficiently to cause a temporary fuel starting of the engine unless means be provided to prevent it. For this purpose a check valve 56 is provided in an enlarged chamber 52 at the junction of channels 38 and 40 and on reduction of suction in the mixing chamber, seats on the bottom of the chamber 52 preventing downward fiow of the fuel.

In addition to the primary fuel nozzles a secondary fuel nozzle 54 is provided in each of the primary mixing chambers and extends upwardly for a considerable distance above the top of the primary nozzle. At relatively high speeds the mixing chamber suction is enough to lift fuel from the secondary fuel nozzles as well as from the primary nozzles but at idling or low speed operation under heavy load, the suction is sufficient to lift fuel only to some point between the top of the primary nozzles and the top of the secondary nozzles so that fuel flows only from the primary nozzles under these conditions. Each primary nozzle is provided with a fuel metering orifice 56 and each secondary with a similar orifice 58. The primary mixing chambers are connected with primary mixture passages 69 by the restricted orifices 62 and the mixture passages 60 are parallel and close together as indicated in Fig. 2 of the drawing. When the carburetor is attached to the manifold these passages register with conduits which convey the primary mixture to the secondary mixing chamber, as fully explained in the above mentioned copending application. Air passages 64 supply air to the primary mixture passages immediately in advance of the restriction 82 as described in the above mentioned Patent No. 1,937,938.

A single throttle valve 66 which extends across all of the primary mixture passages controls the flow therethrough and is provided with grooves 68 which register with the mixture passage. This throttle is operated by means fully disclosed in the above mentioned Patent No. 1,937,938 and which forms no part of the present invention.

All the air entering the carburetor except a small quantity of primary air which is admitted through orifices l8, flows through the air horn 24 and the fiow is controlled by a main air valve 12 normally held against a seat 14 by a spring 16 received between the valve and a flange l8 projecting from a sleeve which is slidably mounted on a stationary guide sleeve 82 fixed in the housing 20 and serving as a guide for the stem 86 to which the air valve is secured in any suitable manner. When it is desired to choke the carburetor to facilitate starting of the engine, the flange '18 is adapted to be lifted by a lever 86 pivoted on a stud 88 fixed in the housing 20 and manually operable by an arm 90 to which is connected some suitable operating connection which extends to a point convenient to the operator of the vehicle. When the choke is operated, the air valve is held closed and sufficient air to carry the starting fuel from the nozzles to the engine is admitted through the orifices H3, previously referred to.

The valve 72 admits air to a main air chamber 92 from which air fiows to the primary mixture passages through an opening 94 in the floor of the air chamber and to the several secondary mixing chambers through a secondary air passage 96 which connects with an inlet in the manifold. A manually operable throttle valve 98 and a suction operated valve H20 secured to shafts I02 and. Hi l respectively, control the flow of air through the passage 96 and the operating connections for these shafts are fully disclosed in the above mentioned Patent No. 1,937,938. On opening of either throttle 63 or 98 the suction in the air chamber 92 is increased when the air valve is opened against the tension of its closing spring to admit additional air and increase the quantity of mixture supplied to the engine. The opening of the air valve must be retarded to some extent, however, to prevent admission of sufficient air to lean the mixture too much. A dash pot is provided to accomplish this result and to prevent fluttering of the air valve. This dash pot forms no part of this invention and is not shown herein but comprises a cylinder formed in the casting 26 and a piston which is secured to the lower end of the air valve stem by any suitable means and slides in the cylinder. Fuel is supplied to the cylinder by leakage around the piston or by a valve controlled port, or in any other suitable way.

In order to enable a better understanding of the present invention which relates primarily to means for controlling the opening movement of the suction operated valve I95, the manner of operation of the two throttles and this valve will be briefly set forth hereinafter. The throttle 66 and the throttle 98 are connected for operation together. The connection includes a lost motion device which permits a predetermined opening of the throttle 66 before any accompanying movement of the valve 98 takes place, the construction being generally such that the throttle 66 can be opened sufficiently to permit an engine speed corresponding to a vehicular speed of approximately twenty miles per hour on the level before the valve 98 begins to open, after which the two valves open simultaneously. No opening movement of the valve Hill can take place until the valve 98 begins to open.

The lost motion device comprises an arm 103 which extends from the throttle valve E6 and is connected by a lost motion linkage 05 to an arm I01 extending from shaft E02. It is not necessary to describe the specific construction of this linkage more particularly as it is no part of this invention. It is shown in Fig. 3, however, and may be of the same construction as that shown in the later patent.

The purpose of the valve Hill is to temporarily retard the fiow of air through the air passage 98 on opening movements of the valve to prevent an increased supply of air reaching the secondary mixing chambers before the increased supply of heavier primary mixture reaches such chambers resulting from the increase in suction to the fuel jets and to increased pressure differential between the outlet and inlet ends of the primary mixture tubes so as to reduce the time necessary for the primary mixture to reach said secondary mixing chambers because of the resulting increase in the velocity of flow through the tubes. The effect of this valve is augmented by means of a fuel pump which comprises a cylinder I 06 in which slides a piston I68 pivotally connected to a rod IIIl which, at its upper end, is pivotally connected to an arm I12 secured to one end of the primary throttle. The delivery conduit I09 from the pump leads to a chamber II4 which communicates with passages Ht, one of which leads to each of the primary mixture passages. The pump supplies some additional fuel on opening of the throttle and the combined effect of both the valve I00 and the fuel pump is such as to supply a mixture which is enriched to the proper degree during the acceleration period following any opening movement of the throttle.

At very high speeds it is unnecessary to sup-- ply a mixture which is enriched to the same degree as it is necessary to supply at lower speeds to secure the desired results and it is the purpose of the present invention to provide means to reduce the retardation of the opening movements of the valve Iilil as the latter approaches its wide open position so that the enriching effect pro duced by this valve is reduced at such high speeds. This result is accomplished by means which will now be described.

In order to retard the opening movement of the valve I09, a cylinder I25] is provided in which there is slidably received a piston I22 to which is pivotally connected a rod I24 which is pivotally connected at its upper end to an arm I28 projecting from the shaft m4 on which the valve E85 is secured. A check valve I28 permits fuel toflow from the fuel bowl to the cylinder E25 through an orifice I30 upon upward movements of the piston I22. Obviously, as the valve Ifiil moves toward open position, the piston I22 is depressed and since the valve I28 is closed on downward movements of this piston, the downward movement thereof is resisted to a considerable extent because the fuel in the cylinder E253 can only escape by leakage around the piston.

In order to reduce the resistance to the downward movement of the piston I22, there is provided in the bottom of the cylinder I20 a metering plug I32, which communicates with a passage I34 formed between a plate I36 secured to the bottom of the casting 26 by machine screws I31 and another plate I38 which is secured to plate I36 in any suitable manner. Communicating with the passage I34 is a small orifice I49 which connects with-a cylinder I42 formed in the casting 26 adjacent the cylinder I86 and having an outlet I44 which is normally closed by a valve I46 held in closed position by a spring I48 received within the cylinder I42 between the valve and the plate I36. This valve has a rod I56 integral therewith and extending upwardly through an orifice in the casting 26 which guides the valve in its vertical movements. This valve is adapted to remain closed until the primary throttle approaches close to its full open position and is then opened by means of an arm I52, which projects from rod IIll which operates the pump piston, and which engages the top of the rod or stem I50.

Obviously as the primary throttle 65 is opened and approachesits full open position, the projecting arm I52 will assume the position shown in dotted lines in Fig. l and will engage the stem I50 to move the valve I45 downwardly and open the port I44 which permits the escape of fuel from the cylinder I20 and greatly reduces the retarding effect of the dash pot which controls the opening movement of the valve IIlEl, permitting said valve to open much more freely and more rapidly after the valve I46 is opened than previously thereto. This will cause the valve Ito to restrict the admission of air to a much less degree upon opening movement of the throttle at very high speeds than it does when said throttle is opened at low and intermediate speeds and hence reduces the enriching effect of such valve on the mixture under such operating conditions.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is. to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movements of the secondary air valve and means operable by the throttle for reducing the retarding eifect of said dash pot on opening movements of the throttle at relatively high engine speeds, by comparison with the eifect of the dash pot at lower speeds.

2. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movements of the secondary air valve and means operable by the throttle for reducing the retarding effect of said dash pot when the throttle reaches nearly full open position toa greater degree than when the throttle is in more nearly closed position.

3. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, the effect of said dash pot being controlled by the position of the throttle at intermediate and high speeds.

i. A charge forming device for internal cornbustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means c'omprising a dash pot for retarding the opening movement of the secondary air valve, a valve for controlling the retarding effect of the dash pot and means operable by the throttle for operating said valve.

5. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, a valve for controlling the retarding effect of the dash pot and means operable by the throttle for opening said valve as the throttle approaches open position.

6. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, a valve for reducing the retarding effect of the dash pot when opened and means operable by the thr ttle for opening the valve as the throttle approaches open position.

7. A charge forming device for internal combusticn engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said a secondary air valve for supplying additional a to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, a pump adapted to supply additional fuel to the mixture passage to also enrich the mixture, means connected to the throttle for operating the pump, and means operated by the pump operating means for reducing the retarding effect of the dash pot under certain operating conditions.

8. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling ineans comprising a dash pot for retarding the opening movement of the secondary air valve, a pump adapted to supply additional fuel to the mixture passage to also enrich the mixture, means connected to the throttle for operating the pump, and means operated by the pump operating means as the throttle approaches open position for reducing the retarding effect of the dash pot.

9. A charge forming device for internal comion engines comprising a mixture passage, means for supplying fuel and air thereto, a throtitroiling the flow of mixture through said .ge, a secondary air valve for supplying additional air to said mixture passage, means for controlling the mixture ratio, said mixture controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, a pump adapted to supply additional fuel the mixture passage to also enrich the mixture, means connected to the throttle for operating the pump, a valve operable to reduce the retarding effect of the dash pot and means operated by the pump operating means for operatsaid valve.

10. A charge forming device for internal combustion engines comprising a primary mixture passage adapted to deliver a primary mixture of fuel and air to a secondary mixing chamber, means for supplying fuel and air to said primary mixture passage, a secondary air passage adapted to supply additional air to the secondary mixing chamber, a secondary air valve in said passage, a primary throttle for controlling the flow through the primary mixture passage, means including said air valve for controlling the mixture ratio under various operating conditions, said ratio controlling means being operable to enrich the mixture on opening movements of the throttle at relatively low speeds and means operable by the throttle for reducing the enriching efiect of said means when the throttle is opened at relatively high speeds.

11. A charge forming device for internal combustion engines comprising a primary mixture passage adapted to deliver a primary mixture of fuel and air to a secondary mixing chamber, means for supplying fuel and air to said primary mixture passage, a secondary air passage adapted to supply additional air to the secondary mixing chamber, a secondary air valve in said passage, a primary throttle for controlling the flow through the primary mixture passage, means for controlling the mixture ratio under various operating conditions, said ratio controlling means comprising a dash pot for retarding the opening movement of the secondary air valve and means operable by the primary throttle for regulating the retarding effect of the dash pct.

12. A charge forming device for internal combustion engines comprising a primary mixture passage adapted to deliver a primary mixture of fuel and air to a secondary mixing chamber, means for supplying fuel and air to said primary mixture passage, a secondary air passage adapted to supply additional air to the secondary mixing chamber, a secondary air valve in said passage, a primary throttle for controlling the flow through the primary mixture passage, means for controlling the mixture ratio under various opcrating conditions, said ratio controlling means comprising a dash pot for retarding the opening movement of the secondary air valve, a valve for controlling the retarding eifect of the dash pot and means operable by the primary throttle for operating said valve as the throttle approaches open position.

13. A charge forming device for internal combustion engines comprising a primary mixture passage adapted to deliver a primary mixture of fuel and air to a secondary mixing chamber, means for supplying fuel and air to said primary mixture passage, a secondary air passage adapted to supply additional air to the secondary mixing chamber, a primary throttle for controlling the flow through the primary mixture passage, a secondary throttle in the secondary air passage, a secondary air valve in said secondary air passage, means for controlling the mixture ratio under various operating conditions comprising means for controlling the opening movements of the secondary air valve on opening of the primary throttle and means operated by the primary throttle for regulating the effect of said controlling means.

14. A charge forming device for internal combustion engines comprising a plurality of primary mixture passages each of which is adapted to deliver a primary mixture of fuel and air to one of a plurality of secondary mixing chambers, means for supplying fuel and air to each of said primary mixture passages, a single primary throttle valve for controlling the flow of mixture through all of said primary mixture passages, a

single secondary air passage adapted to supply air to all of said secondary air passages, a secondary air valve in said secondary air passage, means for controlling the proportions of fuel and air in the mixture formed in all of the secondary mixing chambers comprising means for controlling the opening movement of the secondary air valve and means operated by the primary throttle for variably regulating the effect of said controlling means.

15. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means to enrich the mixture upon opening movements of the throttle comprising a fuel pump and means for retarding the opening of the secondary air valve, and means operable When the throttle approaches full open position to reduce the retarding effect of said retarding means to decrease the degree of mixture enrichment under such operating conditions.

16. A charge forming device for internal combustion engines comprising a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture through said passage, a secondary air valve for supplying additional air to said mixture passage, means to enrich the mixture to a relatively great degree upon opening movements of the throttle at relatively low speeds, said last named means comprising a fuel pump and means for retarding the opening of the secondary air valve, and means operated by the throttle upon opening movements thereof at higher speeds to reduce the effect of said retarding means so as to reduce the enriching effect at high speeds.

1'7. A charge forming device for internal combustion engines comprising, in combination, a mixture. passage, fuel and air inlets therefor, a throttle for regulating the flow of mixture through said passage, a main air valve controlling the admission of air, a secondary air valve for regulating the fuel mixture ratio, means for retarding the opening movement of said secondary air valve to enrich the mixture, and means operable when the secondary air valve approaches its open position to reduce the retarding effect of said retarding means on said air valve.

18. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, fuel and air inlets therefor, a throttle for regulating the flow of mixture through said passage, a main air valve controlling the admission of air, a secondary air valve for regulating the fuel mixture. ratio, means for retarding the opening movement of said secondary air valve to enrich the mixture, a dash pot opposing opening movement of said auxiliary air valve, and means operable when the secondary air valve approaches open position to reduce the resistance offered by said dash pot to the opening of said air valve.

19. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, fuel and air inlets therefor, a throttle for regulating the flow of mixture through said passage, a main air valve controlling the admission of air, a secondary air valve for regulating the fuel mixture ratio, means for retarding the opening movement of said secondary air valve to enrich the mixture, a dash pot opposing opening movement of said secondary air valve, adapted when open to reduce the resistance of the dash pot to opposing movement of the secondary air valve, and means operable when the secondary air valve approaches open position to open the dash pot valve.

20. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuel-air ratio of the mixture sup-plied to the engine, means for retarding the opening of the valve under certain conditions to enrich the mixture, a fuel pump operable to supply additional fuel to also enrich the mixture, and means operable by the fuel pump to control the retarding effect of said retarding means on the said air valve.

21. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuelair ratio of the mixture supplied to the engine, means for retarding the opening of the valve under certain conditions to enrich the mixture, a fuel pump operable to supply additional fuel to also enrich the mixture, and means operable by the fuel pump to reduce the effect of the said retarding means on the air valve as the latter approaches its open position.

22. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuel-air ratio of the mixture supplied to the engine, means for retarding the opening of the valve under certain conditions to enrich the mixture, a fuel pump operable concurrently with the air valve to supply additional fuel to the mixture passage for also enriching the mixture and means operable by the fuel pump as the end of a pumping operation is approached to reduce the retarding effect of said retarding means on said air valve.

23. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuel-air ratio of the mixture supplied to the engine, a dash pot for retarding the opening of the air valve, a valve for controlling the effectiveness of the dash pot, a fuel pump for supplying additional fuel to also enrich said mixture, and means carried by said fuel pump for operating said valve.

24. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuel-air ratio of the mixture supplied to the engine, a dash pot for retarding the opening of the air valve, a valve for controlling the effectiveness of the dash pot, a fuel pump for supplying additional fuel to also enrich said mixture, an operating rod for said fuel pump, and a lug carried by said rod and adapted to engage said last named valve to operate the latter and vary the effectiveness of the dash pot.

25. A charge forming device for internal combustion engines comprising, in combination, a mixture passage, means for supplying fuel and air thereto, a throttle controlling the flow of mixture therethrough, an air valve for regulating the admission of air and for controlling the fuel-air ratio of the mixture supplied to the engine, a dash regulating the admission of air to both the primary mixture passages and air passage, an auxiliary air valve controlling the passage of air through said air passage only and operable to control the ratio of the fuel mixture supplied to the engine, means for retarding the opening movement of the auxiliary air valve to enrich the mixture and means operable when said auxiliary air valve approaches its open position to reduce the retarding effect of said retarding means.

FRED E. ASELTINE. 

